1. Field of the Invention
This invention generally relates to an output device of an information processing system such as facsimile. More in particular, this invention relates to a thermal head device which converts electrical signals into heat signals whereby a thermosensitive paper is brought into contact to obtain a visual image, corresponding to the electrical signals transmitted.
2. Description of the Prior Art
Facsimile machines have been increasingly used to save time in communication between remote places. A facsimile machine includes an output device for converting electrical signals received into visual signals for the ease of understanding the received information. Several different types of such a facsimile output device have been proposed. For example, a well-know electrostatic imaging system, extensively used in electrophotographic copying machines, has been applied to the output device of a facsimile machine. This type of the output device tends to be bulky and requires numerous components, which, in turn, pushes up the manufacturing cost. It is also subjected to the limitation in speed which is inherent to the electrostatic imaging technology.
The current trend is to use a thermal head type output device for converting electrical signals into thermosignals which are applied to a thermosensitive paper for visualization of the electrical information. The thermal head device as the output device of a facsimile machine and the like includes a number of heat-producing resistive elements formed in a single array on a substrate, which elements are individually activated under control. Each of the heat-producing resistive elements, which produce heat in response to electric currents passed therethrough, corresponds to a picture element. Thus, in order to obtain a visualized image of good quality, e.g., high resolution, it is required to provide many picture elements, or resistive elements per unit length. From a practical viewpoint, the resolution of 8 elements/mm will be required, which, in turn, indicates that 1,728 elements must be provided for scanning the width of DIN A4 size paper.
As described above, the thermal head device as an output device for a facsimile and the like are not free from disadvantages which mainly stem from the requirement to provide so many resistive elements. Thus, there is much room for improvements in the thermal head device as proposed herein.